GB919737A - A new method of rock blasting and devices for the purpose - Google Patents

Abstract

919,737. Detonating devices for blasting; explosive and pyrotechnic compositions, IMPERIAL CHEMICAL INDUSTRIES Ltd. Sept. 27, 1961 [Oct. 17, 1960], No. 35462/60. Classes 9 (1) and 9 (2). A detonation initiating device for rock blasting comprises a tubular casing with a watertight closure at both ends, but permitting at one end the insertion of igniter cord which engages a charge 17 of incendiary composition located at that end of the tube. The other end contains the initiating explosive charges of an ordinary detonator, and in an intermediate position is a delay element comprising a charge of slow burning composition 15, which has a burning speed of not more than 10 cm. per minute. Ignition of the charge of incendiary composition by the igniter cord causes ignition of the slowburning composition which, after burning along its length, causes the ignition of the initiating explosive charge and the consequent detonation of the blasting explosive charge adjacent thereto. The igniter cord connects a series of these detonating devices and thus there is a series of explosions, the first of which occurs after the flame of the igniter cord has reached the last detonating device owing to the delay between the flame reaching the device and the actual explosion, produced by the slow burning composition. In one form of the invention the tubular casing consists of two parts; the detonator casing 11 and the connector casing 12 which is constructed to be a sliding fit within 11. A base charge 13 is pressed against the closed end of 11 and charge 14 of initiating explosive is pressed against the base charge. The delay element 15 is located between 14 and a primary charge 16. The connector casing contains at its closed end the charge of incendiary composition 17 slotted at 20 to permit entry of the igniter cord. The casings are crimped together at 19. The casings may be sealed together by means of a waterproof seal or a layer of waterproof sealing may be placed between the overlapping parts of the casing. The delay element may be made of lead and the slow-burning composition of cobalt dinitro bis-ethylenediamine nitrite or a mixture of 65 parts potassium nitrate, 10 parts sulphur and 2 parts of the condensation product of naphthylamine and acetaldehyde prepared as described in Specification 576,107. The incendiary composition may comprise a mixture of red lead, potassium perchlorate, potassium nitrate, silicon, calcium silicide and iron powder, bound together by a composition consisting of nitrocellulose, dibutylphthalate, diphenylamine and citric acid.